Coloured silicon carbide

ABSTRACT

Silicon carbide particles coated with a pigmented coating result in silicon carbide particles which can be used in slip resistant flooring to achieve the desired slip resistance whilst giving improved aesthetic properties. The pigmented coating can be an organic coating such as a two part epoxy system or a water based or solvent based epoxy. Alternatively the pigmented coating can be an inorganic coating such as a ceramic glaze. Also provided are methods of coating silicon carbide particles with either an organic or an inorganic pigmented coating. Further provided are safety flooring materials including silicon carbide particles having a pigmented coating.

[0001] The present invention relates to the production of coated siliconcarbide particles, in particular to pigment coated silicon carbideparticles.

[0002] Silicon carbide, also known as carborundum is a synthetic solidmaterial comprising silicon and carbon. The hardness of silicon carbideis similar to that of diamond. Silicon carbide is producedelectrolytically from graphite and silica under the influence of extremeheat and the product is then crushed to give a wide range of particlesizes.

[0003] Silicon carbide is a particulate material which has a smoothsurface making it reflective and angular edges making it useful inproducts requiring slip resistant properties. Silicon carbide is onlyavailable in two colours which are black and dark green.

[0004] Silicon carbide is used in a variety of industries from grindingwheel manufacture to flooring.

[0005] Silicon carbide, is used to confer slip resistance and wearresistance to a variety of floors including vinyl safety floors. Itsefficacy in achieving slip resistance has meant that its use is verywide spread in slip resistant flooring manufacture.

[0006] In flooring it is preferred to use the black version of thesilicon carbide although it is less pure.

[0007] Being black, and used on the surface of a safety flooring,silicon carbide tends to darken the overall tone of the finishedflooring. This is particularly an issue when high levels are used. Inorder to avoid the tone being darkened excessively, attempts have beenmade to use larger particles of silicon carbide, the idea being that,with larger particles, for a given mass per unit area, fewer particlescan be used to achieve a particular slip resistance. However, with largeblack particles on a light background, the product appears very“functional” and is considered less aesthetically acceptable. Also iflost from the surface, large particles leave large surface voids.

[0008] Some users dislike the high reflectivity of the silicon carbidewhich is considered undesirable for certain applications.

[0009] It would therefore be advantageous to provide silicon carbideparticles in colours other than black or dark green for use in slipresistant flooring to achieve the desired slip resistance whileobtaining improved aesthetic properties.

[0010] Accordingly from a first aspect the present invention providessilicon carbide particles coated with a pigmented coating.

[0011] The coating may be a pigmented organic coating. Alternatively thecoating may be a pigmented inorganic coating.

[0012] Where the pigment is a pigmented organic coating it is preferablya two part epoxy system where the two parts are mixed together toprovide the pigmented organic coating.

[0013] Alternatively the pigmented organic coating may be a water basedor solvent based epoxy or two part solvent based polyurethane orwaterborne polyurethane or acrylic.

[0014] Where the coating is an inorganic coating it is preferably aceramic glaze.

[0015] The silicon carbide particles may be coated with a coupling agentbeneath the pigmented coating to aid adhesion of the pigmented coating.

[0016] The coating of the silicon carbide particles with a pigmentedresin allows a range of colours to be obtained whilst still maintainingthe angular edges of the particles which provide the required slipresistance when used in safety flooring.

[0017] The pigment can be any colour and the colour can be solid ormetallic.

[0018] The silicon carbide particle size range is preferably from 0.2 to0.8 mm.

[0019] According to a second aspect the present invention provides amethod of applying an organic pigmented coating to silicon carbideparticles comprising the steps of:—

[0020] mixing silicon carbide particle with a liquid pigmented organiccoating system; curing the coated particles.

[0021] The coated particles are preferably sieved to remove anyagglomerates. The organic system is preferably a two part system whereinthe two parts are mixed together then mixing with the silicon carbideparticles. The organic coating system is preferably applied at a rate of90-140 g/m² of silicon carbide surface area, most preferably 120 g/m²silicon carbide surface area.

[0022] The method preferably further comprises coating the siliconcarbide particle with a coupling agent before applying the organiccoating system.

[0023] The coupling agent is used to maximise adhesion of the organiccoating system to the silicon carbide particles.

[0024] More than one coating of the organic coating system can beapplied

[0025] In a third aspect the present invention provides a method ofapplying an inorganic pigmented coating to silicon carbide particlescomprising the steps of fusing an inorganic pigmented coating onto thesilicon carbide particles.

[0026] The inorganic coating is preferably a ceramic glaze.

[0027] Preferably the ceramic glaze comprises:

[0028] 1) silicon dioxide which promotes low expansion, high durabilityand abrasion resistance;

[0029] 2) aluminium trioxide which suppresses phase separation andcrystallization and improves acid resistance;

[0030] 3) zirconia as an opacifier and to improve alkali resistance;

[0031] 4) a selection of complex metal oxides as inorganic pigments; and

[0032] 5) a flux to reduce the temperature at which the components ofthe glaze fuse together to form a homogenous mass. The flux preferablyincludes combinations from alkali metal oxides, alkaline earth metaloxides, zinc oxide, boric oxide and lead oxide.

[0033] The alkali metal oxides may include lithium oxide, sodium oxideor potassium oxide.

[0034] The alkaline earth metal oxides may include magnesium oxide,calcium oxide and barium oxide.

[0035] The glaze may be made by mixing and fusing the selectedcomponents in a high temperature furnace to form a glass. The glass ispreferably milled to form a powder known as a frit.

[0036] To coat the silicon dioxide particles with the ceramic glaze thefrit is preferably applied to the particles, the water is removed bydrying at almost 100° C. and the coated particles are then fired attemperatures of from 800° C. to 1400° C., most preferably 1200° C. toremelt the powder and form a glaze.

[0037] The present invention further provides a safety flooring materialincluding the coloured silicon carbide particles of the presentinvention.

[0038] The silicon carbide particles confer slip resistance of thesafety flooring material owing to their angular edges.

[0039] The coloured silicon carbide particles may be the same colour asthe flooring material or alternatively the coloured silicon carbideparticles may be a contrasting colour. The use of coloured siliconcarbide particles means that the desired aesthetic effects can beachieved.

[0040] The safety flooring material could be made from plasticised PVC,plasticised acrylic, rubber, epoxy or polyurethane flow applied resinsystems.

[0041] The present invention will now be described in more detail withreference to the following examples.

[0042] General Particle Coating

[0043] 1. Organic Coating

[0044] The silicon carbide particles are mixed under low shear in aliquid pigmented organic coating, usually after coating with a couplingagent to improve adhesion of the final coating. The organic coating canbe a two component epoxy or alternatively it could be a water based orsolvent based epoxy or two part solvent based polyurethane or waterbornepolyurethane or acrylic.

[0045] The application of frictional heat and/or externally applied heatreduces the viscosity of the coating system, allowing good coveragebefore the onset of curing which is accompanied by a rise in theviscosity. With water based systems the water would first be removed at100° C.

[0046] Full curing is achieved after the coating has fully hardened ontothe silicon carbide and there is no evidence of residual coating liquid.

[0047] The resulting product is then sieved to give correct particlesize distribution.

[0048] Particle agglomeration is avoided by optimising the ratio ofcoating material to silicon carbide and agitation by tumbling orstirring in a rotary action mixer.

[0049] 2. Inorganic Coating

[0050] Inorganic pigmented coatings such as vitreous enamel can be fusedonto the silicon carbide particle at high temperatures.

[0051] Specific Formulations and Method

[0052] 1. Pre-treatment—The silicon carbide particles are coated withthe following coupling agent to maximise adhesion of the final coating.The coupling agent solution is added to the silicon carbide at 0.3 partsper hundred of silicon carbide and blended in a low shear rotary actionmixer before force drying if necessary. Coupling agent formulation Partsby weight A1100 (gamma aminopropyl silane) 50 isopropyl alcohol (IPA) 50

[0053] 2. Coating—A resin system is added to the dried, pre-treatedsilicon carbide whilst mixing. Mixing is continued until the coating iscured. The product is forced dry and post cured if necessary.

[0054] The resin is added at a rate of 120 g per m² of silicon carbidesurface area. Resin System Formulations Parts by weight a) Solvent basedepoxy Part A) Eurepox 7001/75 (75% epoxy in xylene) 420 Methyl isobutylketone 150 Xylene 40 n-butanol 60 pigment/filler 330 Part B) Euredur30/55 (isolated polyamine adduct solution) 245 Xylene 20 Butanol 5 b)Water based epoxy Part A) Eurepox 776 (modified epoxy resin) 45 Pigment16.5 Barytes (barium sulphate) 38.5 Part B) Euredur XE36 (polyamineadduct in water) 40 Water 10 c) Solvent free epoxy Part A) Eurepox 77642 Pigment 16 Barytes 41.6 Antifoam 0.4 Part B) Euredur 43 (acycloaliphatic amine) 25

[0055] In each two part resin system the whole of part A is mixed withthe whole of part B before application to the silicon carbide particles.Typically the particles are mixed with the two part resin system in aribbon or other rotary low shear mixer for about 60 minutes after whichtime the coating on the silicon carbide particles should be hard enoughto handle.

1. Silicon carbide particles coated with a pigmented coating. 2.Particles according to claim 1 wherein the coating is a pigmentedorganic coating.
 3. Particles according to claim 2 wherein the coatingis a two part epoxy system where the two parts are mixed together. 4.Particles according to claim 2 wherein the pigmented organic coating isa water based or solvent based epoxy.
 5. Particles according to claim 2wherein the pigmented organic coating is a two part solvent basedpolyurethane or waterborne polyurethane or acrylic.
 6. Particlesaccording to claim 1 wherein the coating is a pigmented inorganiccoating.
 7. Particles according to claim 6 wherein the coating is aceramic glaze.
 8. Particles according to claim 7 wherein the ceramicglaze comprises: silicon dioxide which promotes low expansion, highdurability and abrasion resistance; aluminium trioxide which suppressesphase separation and crystallization and improves acid resistance;zirconia as an opacifier and to improve alkali resistance; a selectionof complex metal oxides as inorganic pigments; and a flux to reduce thetemperature at which the components of the glaze fuse together to form ahomogenous mass.
 9. Particles according to claim 8 wherein the fluxincludes combinations from alkali metal oxides, alkaline earth metaloxides, zinc oxide, boric oxide and lead oxide.
 10. Particles accordingto claim 9 wherein the alkali metal oxides include lithium oxide, sodiumoxide or potassium oxide.
 11. Particles according to claim 9 wherein thealkaline earth metal oxides include magnesium oxide, calcium oxide andbarium oxide.
 12. Particles according to any preceding claim wherein theparticles are coated with a coupling agent beneath the pigmented coatingto aid adhesion of the pigmented coating.
 13. Particles according to anypreceding claim wherein the particles have a size range of from 0.2 to0.8 mm.
 14. A method of applying an organic pigmented coating to siliconcarbide particles comprising the steps of: mixing silicon carbideparticles with a liquid pigmented organic coating system; curing-thecoated particles.
 15. The method according to claim 14 wherein theorganic coating system is a two part system wherein the two parts aremixed together then mixed with the silicon carbide particles.
 16. Themethod according to claim 14 or claim 15 wherein the organic coatingsystem is applied at a rate of 90-140 g/m² of silicon carbide surfacearea.
 17. The method according to any one of claims 14-16 furthercomprising coating the silicon carbide particle with a coupling agentbefore applying the organic coating system.
 18. A method of applying aninorganic pigmented coating to silicon carbide particles comprising thesteps of fusing an inorganic pigmented coating onto the silicon carbideparticles.
 19. A method according to claim 18 wherein the inorganicpigmented coating is a ceramic glaze made by mixing and fusing theselected components in a high temperature furnace to form a glass.
 20. Amethod according to claim 19 wherein the glass is milled to form apowder known as a frit.
 21. The method according to claim 20 wherein tocoat the silicon dioxide particles with the ceramic glaze the frit isapplied to the particles, the water is removed by drying at almost 100°C. and the coated particles are then fired at temperatures of from 800°C. to 1400° C. to remelt the power and form a glaze.
 22. A safetyflooring material including the coloured silicon carbide particles ofany one of claims 1-13 or made by the methods of claims 14-21.
 23. Thesafety flooring material according to claim 22 wherein the safetyflooring material is made from plasticised PVC, plasticised acrylic,rubber, epoxy or polyurethane flow applied resin systems.